Integrated circuits (ICs) are generally fabricated in an array on or in a semiconductor substrate. ICs generally include several layers formed over the substrate. One or more of the layers may be removed along scribing lanes or streets using a mechanical saw or a laser. After scribing, the substrate may be throughout, sometimes called diced, using a saw or laser to separate the circuit components from one another.
Semiconductor manufacturers have been shrinking transistor sizes in ICs to improve chip performance. This has resulted in increased speed and device density. To facilitate further improvements, semiconductor manufacturers use materials to reduce the capacitance of dielectric layers. For example, to form a finer circuit pattern, a semiconductor wafer having a low dielectric constant (low-k) insulating film is laminated on the surface of the semiconductor substrate. Low-k dielectrics may include, for example, an inorganic material such as SiOF or SiOB or an organic material such as polyimide-based or parylene-based polymer.
However, conventional mechanical and laser cutting methods are not well suited for scribing many advanced finished wafers with, for example, low-K dielectric materials. Relatively low density, lack of mechanical strength and sensitivity to thermal stress make low-k dielectric material very sensitive to stress. Conventional mechanical wafer dicing and scribing techniques are known to cause chips, cracks and other types of defects in low-k materials, thus damaging the IC devices. To reduce these problems, cutting speeds are reduced. However, this severely reduces throughput.
Further, known laser techniques can produce excessive heat and debris. Traditionally, laser pulse widths in the tens of nanoseconds or more have been used for semiconductor cutting or scribing. However, these long pulse widths allow excessive heat diffusion that causes heat affected zones, recast oxide layers, excessive debris and other problems. For example, FIG. 1 is a side view schematic of a semiconductor material 100 diced using a conventional laser cutting technique. Near a cut area 102, a heat affected zone 104 and recast oxide layer 106 has formed. Cracks may form in the heat affected zone 104 and reduce the die break strength of the semiconductor material 100. Thus, reliability and yield are reduced. Further, debris 108 from the cut area 102 is scattered across the surface of the semiconductor material 100 and may, for example, contaminate bond pads.
In addition, conventional laser cutting profiles may suffer from trench backfill of laser ejected material. When the wafer thickness is increased, this backfill becomes more severe and reduces dicing speed. Further, for some materials under many process conditions, the ejected backfill material may be more difficult to remove on subsequent passes than the original target material. Thus, cuts of low quality are created that can damage IC devices and require additional cleaning and/or wide separation of the devices on the substrate.
A method for laser cutting or scribing that increases throughput and improves cut surface or kerf quality is, therefore, desirable.